I have my grandma's KA mixer and a larger one. Both have two bowls (and I often wish for more!). Grandma was a professional cake decorator and had a fleet of four or five KA mixers, so when she died, all of the grandkids got one. She'd replace her KA every few years, but always kept the older ones as a backup. Mine (named Berta, after her) is probably from the 60s. Still works perfectly!
But my mother bought me a larger, new KA two Christmases ago so that I'd have a backup. Berta lives in the garage these days, ready to come out of retirement if my current KA ever has issues. And it's showing signs that that will probably happen this year when I try to mix up my gingerbread house dough (a stiff, tough dough). It overheated and pooped out on me already recently kneading pretzel dough.
Having two KA mixers is a luxury, but having extra bowls and beaters is a must! It makes everything so much more streamlined and easy!